The present invention relates to a hydraulic force booster particularly applicable to actuating master cylinder pistons in brake systems of automotive vehicles, comprising a booster piston and a brake valve disposed in parallel thereto the spring-loaded control piston of which, by a lever system, is displaceable by an actuating rod, with two levers midway of their length, by way of a journal, being pivotably interconnected. The first lever, at the first end thereof, is rigidly supported on the housing and, at the second end thereof, by way of a first coupling, being captured by the actuating rod, and with the second lever, at the first end thereof, is pivotably supported on the booster piston and, at the second end thereof, by way of a second coupling, is in engagement with a set element connected to the control piston. The couplings respectively comprise a coupling element and at least one guiding surface cooperating therewith and including a transverse component.
In a conventional construction of this type (DE-OS No. 08 908), the set element, by way of a sleeve, is rigidly connected to the free end of the control piston of the brake valve. The spring loading the control piston is disposed in the space between the valve body of the brake valve and a stop on the control piston in the vicinity of the sleeve. The second coupling is formed by a cylindrical pin on the set element and by a longitudinal slot provided on the second lever and extending longitudinally of the lever. To safeguard a satisfactory operation of the brake valve and preclude losses, the control piston is seated with a close slide fit in the valve body. The close fit, occasionally, resulted in a locking of the control piston.
It is an object of the invention to provide a hydraulic force booster of the above-described type, minimizing the locking risk of the control piston in the valve body.